I have just purchased and loaded this. Since it is active and monitoring all the time, when/how often should I do system scans?

midnight,
Hello... There are two type of scans that you can have "MWB" perform that have minimal effect on your OS. One is a "Flash Scan", and the other is a "Quick Scan". Both only take a few minutes. You can set these to do this whenever you want ...I have mine set to do this after checking for updates and Downloading \ Installing them... Full scans take a long time to complete, and can be set when convenient, and the PC is no too busy. Read through the screens (tabs) and take your time setting things up the way you want. Regards Fred

One more footnote: The Malwarebytes Flash Scan (available only in their paid version) is meant to be used in real-time and on demand, when you suspect something malicious is attacking your computer. You disconnect from the Internet, and immediately start the Flash Scan. It scans the most critical areas of Windows and comes back with a report or actions to take if something suspicious is going on. A Flash Scan is very quick, taking only a few minutes to complete in most cases. This is not meant to be used for routine Quick Scans, which should be done every few days or daily. MBAM Quick Scans usually take about an hour or less to complete. Full Scans should be done weekly or biweekly, during off-use hours. They can take up to three or four hours on some computers.